An electroencephalograph (EEG) is a known device which senses, measures and records brain waves of a subject person by sensing spontaneous electrical potentials existing at selected scalp sites and generated in the subject's cortex or cerebrum. Usually, an EEG is provided with a plurality of channels, and each EEG channel corresponds to a particular electrode combination attached to the subject. The ERPs sensed at each channel are amplified by a differential amplifier, and the amplifier output signal is recorded.
Historically, the output signal was originally used to control movement of a recording pen on advancing graph paper, as in a polygraph. The polygraph paper is driven at a predetermined rate (e.g., 30 millimeters per second) and is graduated to represent predetermined time increments. The EEG record produced is thus in the form of a long strip of polygraph paper containing a wave form for each EEG channel.
Contemporarily, an EEG can be functionally associated with a computer and the computer's memory device, such as a floppy disc or the like can be used to record the sensed ERPS.
A skilled neurologist can evaluate an EEG record to interpret abnormalities in the wave forms recorded. However, a suitably programmed computer that is functionally associated with an EEG can be used to evaluate EEG sensed signals.
Electrical signals produced by an EEG exhibit different frequencies depending upon the varying electrical activity of the human brain. The EEG signal frequencies detected are conventionally classified into four basic frequency bands, which are generally referred to as "Delta" (0.3-5 Hertz); "Theta" (4 to less than 8 Hertz); "Alpha" (8-13 Hertz); and "Beta" (greater than 13 Hertz). A neurologist or a programmed computer can determine the predominant frequency observed from a particular EEG channel during a particular time period by measuring the time period of the frequency of a given EEG signal wave form.
Since an EEG signal wave form typically includes multiple frequency components, ERP frequency determinations can be complicated procedures. However, electronically produced wave forms and computerized scanning techniques are recognized to substantially improve the objectivity and reliability of brain wave analysis, as those skilled in the art will appreciate. EEG measurable brain waves can be driven by specific extrinsic or endogenous events. For example, a single regularly occurring stimulus will elicit a series of electrical signals or brain waves each time it is presented. The entire series is referred to as an event-related potential (ERP).
Both the frequency of a sensed ERP as well as the amplitude thereof is often analyzed. Significance has been established when brain waves of large amplitudes occur at time intervals of about 300 msec (milliseconds) or more after the eliciting event. One class of brain wave produced under such circumstances is known as P300 brain waves or, sometimes, more simply, as P3 brain waves. The P3 brain wave is a positive deflection in the EEG of a subject electroencephalographically preferably recorded either from the CZ or the PZ cranial positions and with an amplitude typically in the range of about 2 to about 20 microvolts measured from baseline to peak. A P3 wave is recorded in response to stimuli which are especially meaningful to a subject in any way and, in general, the more unexpected and rare the stimulus, the larger the amplitude of the P3 voltage.
Usually P3 is recordable from the CZ, FZ and PZ positions and is characteristically largest at PZ and smallest at FZ. Donchin, E., Ritter, W. and M. Calloway, W. C. (1978), "Event Related Brain Potentials in Man", Calloway et al. ed., Academic Press, 1978. Production of such waves appears to be an involuntary stimulus response.
There is evidence to suggest that the P300 brain wave generating process inherently occurs when the updating or "refreshing", of representations in working memory is required; see, for examples, Donchin, Psychophysiology. 18, 493-513 (1981); Fabiani, Karis and Donchin, Psychophysiology, 22, 588-589 (1985); and others. P300 brain waves of large amplitudes are now recognized to be characteristically elicited by rare or unexpected events, particularly when they are relevant to a task, such as information recognition, that a subject is performing.
It is theorized that reception of such an event by a subject may lead to restructuring or updating of the subject's working memory, and this activity is further theorized to be part of the ongoing process of maintaining accurate schemes of the environment; however, there is no wish to be bound by theory herein. The updating process, according to the theory, may lead to an "activation" of the representation, or to the "marking" of some attribute of the event that was crucial in determining the updating process.
This restructuring of the representation of an event is theorized to facilitate the subsequent recall of the event, by providing valuable retrieval cues. It now appears that the greater the restructuring that follows an individual event, the higher the probability of later recalling that event. If the P300 brain wave amplitude actually represents the degree of restructuring in a working brain memory, then the P300 brain wave amplitude should also characteristically predict capability for later recall. Fabriani, Karis and Donchin, Psychophysiology, 23, 298-308 (1986).
The existing knowledge about the frequency and the amplitude of brain waves and the advent of widespread usage of the programmed computer in behavioral neuroscience has made the analysis of EEG-generated data easier and capable of treatment by new methodology.
Oftentimes, it is desirable to have an objective method of determining whether or not a person has memorized recallable knowledge of a particular fact, whether in a visual or other form, such as factual information concerning a weapon, a crime scene configuration, a secret document, a stolen object, data, another person's face, etc. Such knowledge as taught by certain prior art procedures and devices can be used in "guilty knowledge" assessment tests, a subcategory of procedures used in physiological detection of deception ("lie detection").
If, for example, a discreet, sensorially perceivable stimulus, such as a sound, a light flash, a body tap, or the like is presented to a human subject, his concurrently made electroencephalogram shows a series of time-locked brain wave responses called event related potentials (ERP). It was shown in the 1960's that if a subject is presented with a series or set comprised of stimuli of two types, e.g., a high tone and a low tone, and if either of those tones is presented in, for example, 20 of 100 trials (with the remaining 80 trials containing the other tone), the rare stimulus will cause production of a large ERP identified as a P3 or P300 brain wave, as such is above defined. In this so-called "odd ball" paradigm, it was known that the P3 brain wave amplitude varies proportionally with rarity. Sutton et al., Science, 150 1187-1188 (1965).
In the 1970's and thereafter, other workers reported that a P3 brain wave is produced by a subject when the subject has previously seen such a word (or picture) even when such word (or picture) is also accompanied or by novel or unrelated words (or pictures) relative to the original word or picture. Such unrelated words (or pictures) fail to produce a concurrent P3 brain wave in the subject. Karis et al., Cognitive Psychology, 16. 177-216; Neville et al., Proc. Nat. Ac. Sci. U.S.A.. 79, 2121-2123, (1982).
Sutton (supra) used subject P3 brain wave responses in an odd-ball paradigm procedure which employed simple auditory stimuli, e.g. high tones and low tones, that were presented singly and serially to subjects. Whatever tone was presented least often evoked production of a P3 brain wave response in a subject. Also, Pritchard et al., Psychophysiology, 23, 166-172 (1986) utilized an odd-ball paradigm in which each of the stimuli used was a simple visual flash which differed from others in the set in brightness. R. Johnson, Jr., Ann. of the N.Y. Acad. of Sci., 425, 223-230 (1984), like Pritchard, describe studies utilizing P3 brain wave production in response to memory updating processes, expectancy processes, surprise, perception, and the like.
Fabiani et al., Psychophysiology, 23, 298-308 (1986), and Neville et al. (supra) utilize verbal, meaningful stimuli in a variant kind of odd-ball paradigm bearing on recognition memory; however, these studies were not and could not be configured as fieldrelevant, repetitively presented deception detection odd-ball paradigms because both novel and previously seen words (or pictures) in these studies were never repeated within the EEG run.
The average ERP voltage produced in response to previously seen words (or pictures) was an average of responses to a series of all different words (or pictures). Also, the average ERP voltage produced in response to novel words (or pictures) was an average of responses to all the different novel words (or pictures) comprising the paradigm set used. This kind of paradigm is currently believed to be specifically unsuited for use in real criminal-type investigations since in such investigations it is usually only a single item, such as the murder weapon, the stolen item, the classified document, or the like, which is the crucial evidence involved in a real crime.
The Fabiani et al. and the Neville et al. studies were directed at, and tailored to achieve, scientific elucidation of memory processes. In these studies, the repetition of words was avoided for fear of engaging habituation processes which would tend to reduce P3 brain wave amplitude effects. None of the prior art articles disclose use of an odd-ball paradigm which is serially and repetitively repeated, which is comprised of meaningful word stimuli, and which functions to detect guilty knowledge or other recognition processes.
There are other studies reported in the literature which do not use quasi verbal stimuli which are repeatedly presented. A review of the literature reveals that these studies do not use odd-ball paradigms. In fact, such studies concern memory processes and use with extremely complicated procedures which are tailored to these research purposes. See, for example, the studies reported by Gomer et al., Physio. Psych., 4, 61-65 (1976), (1976); Ford et al., Elect. Clin. Neuroph., 47, 450-459 (1979); Kramer et al., Psychophysiology, 23, 33-47 (1986); and Adam and Collins, Elec. Clin. Neuroph., 44, 147-156 (1978). All such studies actually use "go-no go", or pattern matching, paradigms. In such a paradigm, a set of letters or numbers is memorized by the subject who is then given a trial series in which he decides whether ("go") or not ("no go") a memorized target stimulus is presented. Other differences between these procedures and repetitively presented odd-ball paradigms exist.
Typically, the prior art reports subject P3 brain wave responses to both target and non-target stimuli. Although target P300 brain wave effects are often reported to be bigger, unambiguous use of subject P300 brain wave responses in field investigations of deception requires results which are virtually of the all-or-none kind. Such results are not achievable in the prior art using such paradigms.
Further, the prior art studies use simple stimuli, such as digits or letters, rather than meaningful words, such as are needed for most real-life evaluations. However, the intent of the prior art methods was the elucidation of memory retrieval processes, not the detection of deception. Also, for such memory elucidation research purposes, P3 brain wave latency measurement may have been more important than P3 brain wave amplitude measurement.
Instruments have heretofore been used to determine psychological stress, such as, for example, the apparatus described in U.S. Pat. No. 2,944,542 which relates to a blood pressure measuring device that indicates variations in the velocity of pulse waves, thereby indicating a change in emotional estate. U.S. Pat. No. 3,971,034 describes a method and apparatus for identifying psychological stress by converting oral impulses into electrical signals and recording, observing and analyzing those signals. U.S. Pat. No. 3,893,450 relates to a method and apparatus for examining brain wave form by providing stimuli such as light and determining the characteristic of a mathematically determined point in the brain wave forms of the subject. U.S. Pat. No. 4,188,956 relates to a method of acquiring, compressing and analyzing neurometric test data by means of a digital computer base system. U.S. Pat. No. 4,579,125 relates to a method for processing analog EEG signals to provide an indication of cerebral activity.
None of the teachings of the prior art, however, relate to a method suitable for determining subject P3 brain waves responses from a repeatedly presented stimulus or stimuli interspersed with non. significant stimuli, thereby to obtain reliable results directed towards evaluating control question testing, attention level, pain and other phenomena involving a subject.